[Fix] fix patch_embed and pos_embed mismatch error (#685)

* fix patch_embed and pos_embed mismatch error

* add docstring

* update unittest

* use downsampled image shape

* use tuple

* remove unused parameters and add doc

* fix init weights function

* revise docstring

* Update vit.py

If -> Whether

* fix lint

Co-authored-by: Junjun2016 <hejunjun@sjtu.edu.cn>